1. Field of the Invention
The present invention relates to leveling instruments of the type used in the building and construction trades for determining elevations, alignments and the like.
2. Description of the Prior Art
It is frequently necessary in carpentry, masonry, construction engineering and allied fields to make use of surveying or leveling instruments in order to determine elevations or to insure alignment among a plurality of points or objects at physically separated locations. In some instances, as in the construction of walls and foundations, it is necessary to sight along a line that is as close as possible to a true horizontal. In other cases, as where a drainage ditch or sewage line must have a prescribed drop per running foot, it becomes necessary to sight along a line which has a predetermined inclination with respect to the horizontal.
While professional surveyors' transits are capable of performing the above-described functions, these instruments are usually designed to provide a level of precision that is far beyond that ordinarily required in the building and construction trades. As a consequence, instruments of this type are generally rather complicated, delicate, and expensive. The needs of carpenters, masons and other tradesman, however, call for a leveling instrument which is simple in construction and operation, rugged, and inexpensive. A further and equally important requirement is the ability of the instrument to be quickly and easily assembled and disassembled, and compactly stored, for transport from one job site to the next.
Although a number of leveling instruments have been developed for use in the building and construction trades, those of which the applicant is aware invariably fall short in one or more of the above respects. U.S. Pat. No. 892,217, for example, describes a mason's level in which a sight tube is retained by means of set screws in a pair of sockets formed in the upstanding arms of a U-shaped yoke member. The lower portion of the yoke is pivotally secured by a pivot bolt to a rectangular base which is provided with an annular track for engaging similarly shaped grooves formed in the bottom of the yoke. Threaded openings are provided near the corners of the rectangular base for receiving correspondingly threaded support legs, which enable the device to be mounted and leveled on a suitable support surface. A bubble level device is affixed by screws to the upper side of the sight tube for use in leveling the instrument. While this manner of construction produces a leveling instrument which is, according to its stated objective, simple and inexpensive, the ability of the instrument to be disassembled or "knocked down" for compact storage and transport is impaired by the necessity of loosening or removing a number of threaded fasteners including, at a minimum, the pivot bolt and the four threaded support legs which project from the base.
U.S. Pat. No. 2,900,159 describes a sighting level which includes a spirit level, a sighting tube, and a pivotally articulated support assembly terminating in a C-clamp. The sighting tube is embraced by a pair of clamps which are in turn secured to the upper portion of the spirit level frame by set screws. A similar pair of clamps secures the lower portion of the spirit level frame to the upper of two confronting circular plates which form a part of the support assembly. The lower circular plate is attached by means of a bracket and flat plate member to the C-clamp, which is intended to permit the sighting level to be mounted on a projecting beam or the like. The various components of the support assembly are pivotally interconnected by means of bolts and wing nuts so that the sighting level may be rotated in three orthogonal planes. As before, however, the ability of the instrument to be compactly stored and transported is impaired by the numerous threaded fasteners which must be loosened or removed in order to separate the sighting level into its component parts. Moreover, the use of a C-clamp as the ultimate support device for the sighting level requires the presence at the job site of an additional support member, such as a fence or a saw horse, to which the C-clamp can be affixed, and may therefore limit the versatility of the instrument.